All allergic conditions are increasing, with about one in three people in the UK suffering from an allergy-related problem some time in their life.

For many, this may be little more than a mild source of irritation but for others, it can be a life-threatening experience.

Common allergies include asthma, hay fever, eczema, wasp stings, medication and food allergies.

Four out of ten children have at least one allergy and one in five has asthma.

Statistics show about six million people have eczema, while more than nine million suffer from hay fever and one million have a food allergy.

Student Sarah Quinnell, 22, from Brighton, has to be continously on her guard because she is allergic to a range of food, including tomatoes, citrus fruits, shellfish, nuts and caffeine.

Strawberries and melons are also to be avoided.

As a child, she suffered from asthma and had minor allergies to strawberries and penicillin but these gradually faded.

Out of the blue, two years ago, Sarah suffered an extreme anaphylactic shock and was rushed to hospital.

She now suffers allergic reactions on a regular basis and has ended up in hospital seven times in the past year.

Sarah carries a special pen, which injects adrenalin for emergencies, and is waiting to have a rare type of blood test to show whether her body contains something which inhibits her natural antihistamine protection.

Different allergies can cause different conditions with a wide range of possible symptoms, including itchy skin and eyes, rashes, sneezing, a runny nose, coughing, wheezing and shortness of breath, swelling of the mouth, sore throat, vomiting or diarrhoea.

Anaphylactic shock is a sudden, catastrophic allergic reaction involving the whole body. Prompt medical treatment is essential.

Without it, the heart and circulation may fail, which could prove fatal.

Medical experts are not sure why some people develop this condition but it usually happens to people who are already known to have allergies.

The most common cause of anaphylactic shock is eating a food which causes an allergic reaction, with peanuts and other nuts such as almonds, brazils, hazelnuts and walnuts most likely to be the culprit.

The condition can be brought on by fish, shellfish, eggs and dairy products.

Even eating a tiny amount of a particular food can cause this shock reaction.

Allergy to venom from bee and wasp stings can also be a trigger, as can an allergy to latex and drugs such as antibiotics.

The initial reaction is swelling and itching of the area which the allergen has entered. Food, for example, initially causes swelling and itching of the mouth and throat, while a wasp sting will cause intense itching and swelling at the sting site.

A generalised reaction then rapidly follows, with an itchy rash which spreads over the whole body. The face and soft tissues begin to swell and breathing becomes difficult.

The sufferer gets very agitated and blood pressure begins to drop. At this point, the patient collapses and loses consciousness.

These symptoms develop very rapidly. Health experts say it is vital patients with this extreme reaction are given adrenalin quickly. The drug raises blood pressure, eases breathing difficulties and reduces swelling.

Food allergies are a difficult area for doctors to pinpoint because there are so many possible reactions to so many foods.

Common allergies in children are triggered by cows milk, wheat and peanuts, while in adults, it tends to be nuts, fruits and seafood.

Asthma is another common allergy and affects the small airways which carry air in and out of the lungs.

An allergy to house dust mites, mould spores, pollen, pets and some food can trigger the condition. Most people find several things bring on their asthma.

Asthma is also caused by viral infections such as colds and flu; cigarette smoking in the home; certain forms of exercise, such as running; exposure to cold, dry air; medication which contains aspirin; and drinks with sulphur dioxide.

For more details, call the Allergy UK helpline on 020 8303 8583 or visit the web site at www.allergyuk.org